In modem communication systems for voice a telephone number and/or a name of a communication partner can usually be shown on the display of a telephone for incoming and outgoing calls.
To transfer the telephone number, in ISDN-based protocols (ISDN: Integrated Services Digital Network) a method known as CLIP (Calling Line Identification Presentation) is used to display a caller's telephone number. Frequently however a name assigned to a subscriber is not transferred at the same time.
For terminals in private networks the terminals and their telephone numbers are frequently assigned names and configured by the private branch exchange system. Within the framework of a connection between two terminals of the private branch exchange the configured name of the respective communication partner is additionally transferred to the terminals and is displayed on the respective terminals. If on the other hand a connection is established via a trunk line from an external communication partner of another private or public network to an internal communication partner within the private branch exchange, the private branch exchange cannot usually display the name of the communication partner external to the private branch exchange, since only data for the terminals of the private branch exchange is configured in the private branch exchange.
Furthermore modern terminals frequently have an internal memory for displaying the name of a communication partner, in which an assignment of telephone number to name is stored, with these types of assignment being entered manually by the user of the terminal. For an incoming call the name associated with the telephone number signaled can be determined by these types of terminal and can be displayed on a screen of the terminal. This method is mostly implemented for mobile radio terminals of a mobile radio network or ISDN terminals of a public telephone network, since only the telephone number is usually transferred in these networks with no transfer of the name.